The research published Monday in Current Biology suggests that large dinosaurs made a significant contribution to the greenhouse effect back then. Study author David Wilkinson of Liverpool John Moores University in England estimated that about 570 million tons of methane came from dinosaurs. That’s similar to total atmospheric levels of methane today produced by livestock, farming and industry. Cows alone now produce nearly 100 tons a year of methane.

And you thought the subway smelled bad.

The study looks at the biggest — and presumably gassiest — dinosaurs, called sauropods. These were the long-necked plant eaters that munched on the top of trees. They were large animals that had food fermenting in their guts for long periods of time because of their giant size, said University of Maryland paleontologist Thomas Holtz, who wasn’t part of the study.

Wilkinson said dinosaur gas was just one factor at a time when the world was quite tropical, about 18 degrees warmer than now. But he said some in the media and blogosphere have misinterpreted his study to say it was the main cause of ancient warming. In a phone interview, Wilkinson said it was only one of the causes, but dinosaur gas “is big enough to be a measurable effect.”

What caused the ancient pre-human world to be so hot — just the way the dinosaurs needed it — was a variety of factors. Volcanoes spewed much more greenhouse gases than now, Holtz said. Swamps, water currents, shallow seas and plentiful plankton combined to raise greenhouse gas levels far higher than today, he said.

Outside climate experts say the study makes some sense, but that the warming from dinosaur gas back then is dwarfed by man-made carbon dioxide today from industry.

NASA climate scientist Gavin Schmidt quickly ran some calculations based on Wilkinson’s figures. Dinosaur methane would have hiked temperatures about half a degree, which is a fraction of what’s been caused by the burning of fossil fuels like coal and oil in the 20th Century, he said.

It’s also wrong to suggest the study blames dinosaur flatulence for their extinction, Holtz said. He noted that the sauropods started showing up — and getting gassy — around 200 million years ago and didn’t die off until 65 million years ago.

University of Victoria climate scientist Andrew Weaver said: “Frankly, methane emissions from dinosaur burps is probably not the No. 1 thing we should be concerned about in modern society.”